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In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases. Nucleophilic describes the affinity of a nucleophile to bond with positively charged ...
The most common Lewis bases are anions. The strength of Lewis basicity correlates with the pK a of the parent acid: acids with high pK a 's give good Lewis bases. As usual, a weaker acid has a stronger conjugate base. Examples of Lewis bases based on the general definition of electron pair donor include: simple anions, such as H − and F −
The ECW model is quantitative model that describes and predicts the strength of Lewis acid base interactions, -ΔH . The model assigned E and C parameters to many Lewis acids and bases. Each acid is characterized by an E A and a C A. Each base is likewise characterized by its own E B and C B. The E and C parameters refer, respectively, to the ...
As the name suggests, a non-nucleophilic base is a sterically hindered organic base that is a poor nucleophile.Normal bases are also nucleophiles, but often chemists seek the proton-removing ability of a base without any other functions.
G. N. Lewis realized that water, ammonia, and other bases can form a bond with a proton due to the unshared pair of electrons that the bases possess. [3] In the Lewis theory , a base is an electron pair donor which can share a pair of electrons with an electron acceptor which is described as a Lewis acid. [ 4 ]
Here, a strong Lewis acid is required to generate either a carbocation from an alkyl halide in the Friedel-Crafts alkylation reaction or an acylium ion from an acyl halide. In the vast majority of cases, reactions that involve leaving group activation generate a cation in a separate step, before either nucleophilic attack or elimination.
Bases are defined by the Brønsted–Lowry theory as chemical substances that can accept a proton, i.e., a hydrogen ion. In water this is equivalent to a hydronium ion). The Lewis theory instead defines a Base as an electron-pair donor. The Lewis definition is broader — all Brønsted–Lowry bases are also Lewis bases.
with regards to acid-base reactions, electron-rich species have high pKa's and react with weak Lewis acids. [ 4 ] with regards to nucleophilic substitution reactions , electron-rich species are relatively strong nucleophiles, as judged by rates of attack by electrophiles.